Technical Field
The present invention relates to a micromini built-in circuit breaker for use in, for example, secondary battery packs of electric devices and the like.
Background Art
In various electric devices, a circuit breaker is employed as a protective means (safety circuit) for a secondary battery, an electric motor or the like of such electric device. The circuit breaker cuts off the electric current in order to protect the secondary battery, the electric motor or the like if an abnormality has occurred, for example, the temperature of the secondary battery has overly increased during discharging or charging, or an overcurrent has flowed in the electric motor incorporated in a machine such as automobile, home electric appliance and the like,
Such circuit breaker used as a protective means is required to operate accurately responding to a temperature change (to have good temperature characteristic) and to show a stable low electric resistance in its conduction state or closed state.
The circuit breaker includes a thermal actuator element for opening or closing the electrical contacts according to the temperature change.
In the international patent application publication No. WO2011/105175 (hereinafter, patent literature 1), a circuit breaker is disclosed, wherein a bimetal is used as the thermal actuator element. The bimetal is, as well known, composed of two layers of metals which has different coefficients of thermal expansion and which are joined together. According to a temperature change, the bimetal changes its shape, and the thermal actuator element using such bimetal can control the opened or closed state of the electrical contacts of the circuit breaker.
Components of the circuit breaker such as the thermal actuator element, a PTC thermistor, a movable-contact piece, and a fixed-contact piece are housed in a package.
In order to use the circuit breaker, a terminal of the fixed-contact piece and a terminal of the movable-contact piece are connected to an electric circuit of an electric device.
In the circuit breaker disclosed in the patent literature 1, the fixed-contact piece is integrated with a main body of the package (resinous base) through an insert molding technique. (cf. paragraph [0031] of patent literature 1)